1. Technical Field
The embodiments relate generally to power efficiency in power supply systems.
2. Description of Related Art
Engineers have historically used DC power supplies to act as a buffer between the equipment requiring electrical power and the primary electric power source. In the United States and many other nations, electric power is usually transmitted using AC power, which, in turn, requires some form of an AC/DC converter to convert the delivered AC power to a form that the equipment can properly use. Switching-mode DC power supplies convert AC voltage to DC voltage using components with low losses in power dissipation, such as capacitors, inductors, transformers, and switches (transistors, diodes etc).
The efficiency of a switching mode power supply (SMPS) varies depending on the load. For example, a SMPS operates at a much higher efficiency when fully loaded than at low loads. There are three main areas where one can increase efficiency for any given circuit: (1) current harmonics drawn from the main source (power factor), (2) component losses, and (3) architecture of the system.
In an effort to lower the harmonics involved when converting AC power drawn from the main source to DC power delivered to the load, engineers regularly use some form of Power Factor Correction (PFC) to increase the amount of real power delivered to the device. One form of such power factor correction involves the use of a power electronic circuit that controls the amount of power drawn by a load in order to obtain a power factor near unity.
For switched mode power supplies, engineers use a boost converter as a DC/DC power factor correction converter between the rectifier and the load, as it maintains a constant DC bus voltage on its output while drawing current that is always in phase with and at the same frequency as the line voltage. However, a boost converter only creates a higher-voltage regulated DC output, which also requires another switch-mode converter in series with the boost converter to produce the desired output voltage from the DC bus for use with other devices.
This topology may increase power factor, but it does not optimize the overall power efficiency of the whole system, as it does not address the system architecture or component losses. For example, the operating set points, the input and output voltages of the first and second converters, may not be optimized with each other to minimize power dissipation within the whole system. This is because two main sources of power dissipation in component losses, conduction losses and switching losses are dependent upon current and voltage respectively. For a given output power, current and voltage are inversely proportional, so that minimizing one power loss may create an unacceptable value for other power losses.
The device receiving the rectified DC power of the system may also operate at different states. For example, a telecommunications device may operate in an “active” stage and a “standby” stage that require the system to delivering varying DC power. Therefore an AC/DC conversion system may need to use differing operating set point dependent upon the voltage actually required by the load; a value that may vary over time.
Based on the prior art, there is therefore a need for an AC/DC power conversion system that maximizes the power efficiency of the entire system while also operating safely within the parameters of the components comprising the system. The system also needs to adjust dynamically to any changes in the load that may require varying operating set points based on the AC feed signal input and the DC supply signal output.